If you burn your toast once it's an accident. But if you keep doing it... well, you might change the settings on your toaster.
So it is with England's bowlers. There are now four men associated with this England team - Mason Crane, Tom Curran, Ben Stokes and Mark Wood - who have all thought they had taken a maiden Test wicket only to see the joy snatched from them with the realisation they have bowled a no-ball.
There are various theories as to why this might be happening. One of them, suggested by Jonny Bairstow at the close of play on Saturday and James Anderson earlier in the series, was that the adrenalin inherent in playing such a big match lures bowlers into straining just a little more than normal. Another suggests that on-field umpires at most levels of the game have prioritised other facets of the job so rarely check for no-balls with the rigour they once did. As a result, bowlers can slip into bad habits.
There's some logic, no doubt, in both theories.
But if something keeps happening, it can't be dismissed as an aberration or accident. It has become a pattern. And if a pattern has emerged, it is time for the coaching staff to take action to change it.
Nobody who regularly watches England training can be surprised by these no-balls. The bowlers habitually overstep in the nets. Almost every delivery. While there are times when a coach might stand in the position of the umpire and ensure the bowlers' front foot remains behind the line, it happens rarely. As a result, those bad habits can become engrained.
It seems an oddly sloppy approach to such an important part of the game. After all, England would have increased the percentage of wickets they claimed on the third day in Sydney by 50 percent if Crane had not overstepped when bowling to Usman Khawaja.
In a discipline like bowling where repeatability is valued, it stands to reason that it should extend to run-ups. Most modern bowlers measure their run-ups with tape before games, so why not ensure they are identical in training? And why not groove that run-up, like a hurdler or long-jumper, in a bid to cut down the number of no-balls? Why not approach the issue with discipline and attention to detail and try to prevent a fifth bowler joining the club?
Given the sheer number of support staff travelling with the England squad these days - the butcher, the baker, the tropical fishmonger - you would think one of them could be employed to stand in the nets, watch the front line and bellow "no ball" when required.
Maybe it wouldn't entirely rid England of the problem, but it might well improve it. And it costs nothing.
If you burn your toast once it's an accident. But if you keep doing it... well, you're a bit of an idiot.
"In an ideal world everyone is behind the line but it's not the first time it's happened and it definitely won't be the last," Bairstow said.
Meanwhile Bairstow - amid praising Moeen Ali for his "outstanding" bowling, Anderson for his "lovely" bowling and Crane for bowling "nicely"; really you wonder how many Australia would score if England bowled poorly - said that, given his time again, he would still elect to forego a nightwatchman on the first evening of this match and come out to bat.
"I genuinely don't regret it," he said. "I've faced the new ball many times and you've got a nightwatchman who has not faced Mitchell Starc. I had 18 balls to survive. I'm backing myself to face half the balls, if not all of them. There was a new ball, they had two guys in Starc and Josh Hazlewood who use it effectively."
Bairstow also defended the stroke that brought his dismissal - pushing firmly at what turned out to be the final ball of the day.
"No one was complaining when I hit the one for four two balls earlier," he said. "It got me out and was skilfully executed. Live by the sword, die by the sword. I don't think it's a massive issue."
As England spent another day in the field, though, as they faced the prospect of yet another first innings that stretched beyond 150 overs, the thought occurred: Australia's batsmen sell their wickets far more dearly than England's.
Nobody tells them they are promising when they are dismissed for 25. Nobody pretends that is good enough. England, in training, in batting, in their self-appraisals, are starting to sound just a little bit soft.
George Dobell is a senior correspondent at ESPNcricinfo